The present invention relates to improvements in cutting/sealing devices for plastic bag making machines.
Prior art bag making machines commonly are of a type consisting of a rectangular base frame provided at one of its ends with a support member for a spool of printed and folded or molded plastic film, a sequence of rolls extending from the spool support member and also mounted on the base frame and disposed up to the middle of the latter. In this area, the cutting/sealing device is transversely disposed to receive the traveling plastic film between its two sections, whereby the film is cut and sealed to form the plastic bag. The thus formed bag leaves the cutting/sealing area of the device on an endless belt conveyor traveling on the base frame to be collected at the edge of the other base frame end.
Known cutting/sealing devices consist essentially of an upper section and a lower section of identical construction which are aligned vertically, one of them operating in a guillotine-like manner and being actuated like cams connected to the machine motor. The plastic film to be cut and sealed travels horizontally between the two sections, perpendicularly to their common axis, the cutting/sealing action being performed by means embodied in the device.
Each section forming the device comprises essentially a sealing bar of trapezoidal cross section which seats on a heating bar, the latter resting on a support member. The sealing bar and heating bar are provided in their opposing faces with a longitudinal channel-like member. The downstream portions of the channel-like members are heated by an electrical resistance element located in a duct between the sealing and heating bars, the downstream portions comprising the sealing surfaces for sealing the plastic bag after it has been cut by a knife member located in the channel-like member of the lower sealing bar.
The so-constructed sealing bars are coated with a teflon film, the main purpose of which is to cover the sealing surfaces. The teflon film is secured to the side faces of the sealing bar by a plurality of bolts and extends therefrom through the sealing surfaces and into the channel-like member. In the channel-like member, the teflon film is secured to the upper sealing bar by means of a rod-like stretcher which lies at the bottom of the channel-like member. The teflon film is also secured to the lower sealing bar by means of a rod-like knife member support located at the bottom of the channel-like member.
The teflon film becomes warn out by continued use and requires replacement. In the known cutting/sealing devices where the film is secured by a plurality of bolts, a stretcher and a knife member support, relacing the film becomes a burdensome task in that removal and remounting of all of the fixing elements is required, resulting in excessive down time for the machine and consequent economic loss.
Having the above disadvantages in mind, this invention provides improvements in the cutting/sealing device for plastic bag making machines, and a major object of the invention is to provide the device with means which allow replacement of the teflon film without the need for handling so many screws and components, thus significantly shortening the machine down time.
The plastic film used to form the bag is available to bag manufacturers in two basic forms. In one form, the film is supplied as a plastic sheet folded longitudinally and in the other form the plastic film is molded into a tubular form.
The known cutting/sealing devices require troublesome changes and adjustments to handle either form of plastic film, thus causing long machine down times.
Therefore, a second objective of the invention is to provide a cutting/sealing device having means which permits manufacturing plastic bags from either form of presentation of the plastic film, always having in mind a minimizing of machine down time.
A very frequent problem arising with known cutting/sealing devices for plastic bag making machines is buckling resulting from excessive heating of the sealing bars. Such buckling effect in the cutting/sealing device causes defective sealing of the plastic bags and generalized malfunction of the unit. It is therefore another object of the invention to provide means to avoid or straighten out any buckling of the cutting/sealing device.